The present invention relates to fiber packets for modifying castable compositions such as concrete, and particularly to fiber packets formed by collating, cutting, and separably-binding the cut fiber ends together along the plane defined by the cut ends using a binding material that is dispersible within the castable composition. The integral packet facilitates introduction of fibers into, and their subsequent dispersal and substantially uniform distribution within, the castable composition.
It is well known in the construction industry to add fibers to fresh concrete to improve characteristics of the resulting hardened concrete structure. Fibers, such as steel, glass, or synthetic materials are typically added to the mixture. See e.g., U.S. Pat. No. 4,665,109 of Pedersen et al.; U.S. Pat. No. 4,426,458 of Woodhams et al.; and U.S. Pat. No. 4,210,009 of Farfor et al., all of which are incorporated herein by reference. Fiber-reinforced concretes are said to have improved fracture toughness as well as a retarded degree of crack propagation.
In the past, concrete-reinforcing fibers have been packaged and sold in polyethylene bags. The bags were added to the concrete mixture by opening the plastic bags and shoveling or dumping fibers directly into a concrete mixer or similar apparatus during the concrete mixing operation. This labor-intensive task is often messy and can result in a non-uniform dispersion of fibers when clumps of fibers become encased in the fresh concrete mixture and resist wetting due to their hydrophobic nature.
U.S. Pat. No. 4,961,790 of Smith et al. discloses a water-soluble bag for introducing reinforcing fibers into concrete. In the aqueous concrete environment, the bag purportedly dissolves and releases the fibers into the concrete.
U.S. Pat. No. 5,224,774 of Valle et al. discloses a non-water-soluble paper packaging system for introducing fibers into an aqueous concrete mixture. The non-water-soluble package is ruptured by the mixing action of concrete, which contains sand and gravel, so that the fibers are released and uniformly distributed throughout the concrete. Clumping of the package is avoided because the non-water-soluble paper packaging material is abraded by the aggregates in the concrete mixing operation.
U.S. Pat. No. 5,807,458 of Sanders et al. discloses fibers which are bundled using a circumferential perimeter wrap. The perimeter wrap must be maintained under sufficient tension to restrict lateral movement of the fibers relative to one another. The perimeter-wrapped bundles are cylindrical and fabricated from a fiber tow or a hank by wrapping the tow or hank with a strip of material in a spiral overlap manner and then cutting the wrapped fibers to provide separate cylindrical fiber bundles. The perimeter wrap comprises a water dispersible material to maintain initial integrity. Sanders et al. state that upon disruption of the continuity of the perimeter wrap and the resulting tension maintained on the reinforcing fibers, the fibers are then rapidly dispersed into the cementitious mixture with minimal, if any, agglomeration because the fibers are maintained in a substantially parallel arrangement on release.
It is an objective of the present invention to facilitate the introduction of a plurality of fibers into a castable composition (such as wet concrete) using a xe2x80x9cpacketingxe2x80x9d rather than perimeter-wrap bundling means, and, upon agitation of the castable composition, to separate individual fibers from the packeting, and to obtain dispersal of the fibers within, and substantially uniform distribution of the individual fibers throughout, the castable composition.
In surmounting the disadvantages of the prior art and providing improved fiber systems for use in modifying castable compositions, such as concrete, the present invention provides novel fiber packets having improved convenience in packaging, handling, shipment and transportation, dosing, and ease of use.
An exemplary fiber packet of the invention comprises a plurality of fibers arranged in side-by-side manner, the plurality of fibers being cut perpendicularly to obtain terminal cut ends, and the terminal cut fiber ends being separably-binded together along a plane defined by said terminal cut fiber ends. The term xe2x80x9cseparably-binded,xe2x80x9d as used herein, means that the fiber ends are bonded or adhered together using a dispersible binder material. Upon agitation of the castable composition, the fiber ends are separable due to the abrading action of the aggregates in the composition and/or the dissolving action of the aqueous mixture on the binding material.
An exemplary binder material for separably-binding the fiber ends may include a polysaccharide, gelatin, poly(meth)acrylic acid, wax, or a mixture thereof. In one exemplary process of the invention, a hot wax (e.g., in thermally softened form) can be spray applied or coated across the cut terminal ends of the fibers and allowed to solidify to bind the fiber ends together. In other exemplary embodiments, the cut fiber ends may be separably-bonded together such as by using a water-swellable or water-dispersible binder material. Conventional adhesive materials, such as pressure-sensitive adhesive or hot-melt adhesive, may also be used. For example, the fiber packets may be formed by using conventional masking tape (e.g., a paper carrier layer having an adhesive layer such as an elastomeric material, e.g., a butyl rubber-based adhesive, or other conventional adhesive material).
An exemplary process of the invention for packeting a plurality of fibers comprises providing a plurality of fibers in a side-by-side manner, cutting the fibers perpendicularly to obtain cut terminal ends, and separably-bonding together the fibers along a plane defined by the cut terminal ends.